Bootstrap modal not working in material theme OPENWRT

I'm using luci material theme. I have also added links required for bootstrap 4. I'm unable to use modal for confirmation boxes while clicking Logout.
I get error in opening the site.
/usr/lib/lua/luci/dispatcher.lua:284: No valid theme found
stack traceback:
[C]: in function 'assert'
/usr/lib/lua/luci/dispatcher.lua:284: in function 'dispatch'
/usr/lib/lua/luci/dispatcher.lua:195: in function </usr/lib/lua/luci/dispatcher.lua:194>